I've followed the Dropbox instructions for setting up single sign-on with ADFS 3.0. The step-by-step guide is perfect, but so far, I have not been able to get it to work.
I've created the Relying Party Trust as instructed, setup the rules, exported our existing token signing certificate (without the private key) and followed the steps for enabling SSO (optional) from our admin portal.
When I try to sign in to Dropbox afterwards, I enter my email address and it recognizes we have single sign-on setup but when it tries to redirect me to our Idp, I get "the web page cannot be found" with the URL below. I've specified the same sign-in URL as the one we use with Office 365, which is also working with ADFS 3.0.